Add more safety around message reference misuse

message.go

@@ -120,7 +120,9 @@ type Message struct {
 	// Is sent with Rich Presence-related chat embeds
 	Application *MessageApplication `json:"application"`
 
-	// MessageReference contains reference data sent with crossposted messages
+	// MessageReference contains reference data sent with crossposted or reply messages.
+	// This does not contain the reference *to* this message; this is for when *this* message references another.
+	// To generate a reference to this message, use (*Message).Reference().
 	MessageReference *MessageReference `json:"message_reference"`
 
 	// The flags of the message, which describe extra features of a message.

restapi.go

@@ -1612,6 +1612,9 @@ func (s *Session) ChannelMessageSendEmbed(channelID string, embed *MessageEmbed)
 // content   : The message to send.
 // reference : The message reference to send.
 func (s *Session) ChannelMessageSendReply(channelID string, content string, reference *MessageReference) (*Message, error) {
+	if reference == nil {
+		return nil, fmt.Errorf("reply attempted with nil message reference")
+	}
 	return s.ChannelMessageSendComplex(channelID, &MessageSend{
 		Content:   content,
 		Reference: reference,